Many aspects of the immune response depend upon precise cell movements and cell interactions which appear to be under some form of transmembrane control exerted through cell surface receptors. Considerable indirect evidence suggests that intracellular contractile proteins or cytoskeletal elements are the effectors of various forms of cell movement. The recognition that membrane events which occur during ligand-triggered translocation and endocytosis of cell surface receptors have striking similarities to those which appear to occur during other types of receptor controlled movements has generated this proposal to biochemically evaluate the role of contractile proteins in translation and endocytosis of immunologically important receptors on lymphocyte membranes. The plan is to measure the interaction of contractile components with the lymphocyte membrane and to determine the effect of ligand-cell surface receptor complex formation on these interactions. Two complementary approaches will be used in the analysis: 1) Isolation and functional charcterization of components of the lymphocyte contractile complex. Particular emphasis is to be placed on analysis of proteins which control the assembly of actin, myosin, and tropomyosin and their interactions with the cell membrane. 2) Analysis by direct binding studies and by immunofluorescence of the interactions of contractile components with the cell membrane and of the effect of ligand-receptor complexes on these interactions.